To control an operation of, for example, a walking aid apparatus for assisting a human being in walking or to control a traveling motion of a biped walking robot, it is necessary to successively grasp the floor reaction forces acting on legs of the human being or the biped walking robot (to be more specific, the forces from a floor that act on ground contact portions of the legs) and the positions of floor reaction force acting points. Grasping the floor reaction forces and the floor reaction force acting points makes it possible to grasp moments or the like acting on joints of the legs of the bipedal walking mobile body, and to decide target auxiliary forces of the walking aid apparatus or desired drive torques or the like of joints of the biped walking robot on the basis of the grasped moments or the like.
As a technique for grasping the floor reaction forces, one disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2000-249570, has been known. According to this technique, a floor reaction force of each leg is grasped as a resultant value (linear combination) of a plurality of trigonometric functions having mutually different cycles of 1/n (n=1, 2, . . . ) of a walking cycle, because time-dependent change waveforms of floor reaction forces of each leg periodically change during steady walking of a biped walking body. According to this technique, however, the positions of floor reaction force acting points cannot be grasped, making the technique inadequate for grasping moments acting on the joints of legs of the biped walking mobile body.
There has been also known a technique in which a biped walking mobile body is walked on a force plate installed on a floor so as to grasp floor reaction forces and the positions of floor reaction force acting points on the basis of the outputs of the force plate (refer to, for example, Japanese Unexamined Patent Application Publication No. 2001-29329).
This technique, however, presents a problem in that the floor reaction forces and the positions of floor reaction force acting points can be grasped only in an environment wherein a force plate is installed, so that the technique cannot be applied to the walking of a biped walking mobile body in a normal environment.
Accordingly, the present applicant has previously proposed in, for example, Japanese Patent Application No. 2002-18798 (Japanese Unexamined Patent Application Publication No. 2003-220584), a technique that permits real-time estimation of the positions of floor reaction force acting points. This technique uses the fact that the inclination angle of a thigh of each leg or the bending angle of a knee joint has a relatively high correlation with the position of a floor reaction force acting point with respect to the ankle of each leg (the positional vector of a floor reaction force acting point, using the ankle as the reference). More specifically, according to the technique, the correlation data (e.g., data tables or arithmetic expressions) showing the correlation between the inclination angles of thighs or the bending angles of knee joints and the positions of floor reaction force acting points is created and stored beforehand, and the positions of floor reaction force acting points are estimated from the correlation data and the inclination angles of thighs or the bending angles of knee joints measured while a biped walking mobile body is walking.
However, further experiment and study by the inventors of the present application, it has been revealed that the correlation between the inclination angles of thighs or the bending angles of knee joints and the positions of floor reaction force acting points is influenced by the walking speed or the like of a biped walking mobile body and further influenced by the motion modes of a biped walking mobile body, such as a level-ground walking mode, a staircase walking mode, and a slope walking mode. Hence, in order to properly estimate the positions of the floor reaction force acting points by the aforementioned technique, it is necessary to prepare a plurality of types of the above correlation data for each walking speed or motion mode of the biped walking mobile body and to retain them in a memory. This has been inconveniently taking up a major part of the capacity of the memory. There has been another inconvenience in that, when a motion mode is changed over, discontinuity in position of a floor reaction force acting point estimated on the basis of another correlation data before or after the changeover is likely to occur, resulting in a discontinuously changed estimated value of a joint moment when the estimated position of the floor reaction force acting point is used to estimate the joint moment.
The present invention has been made in view of the above background, and it is an object of the present invention to provide a floor reaction force acting point estimating method that makes it possible to grasp, in real time, the position of a floor reaction force acting point by a relatively simple technique without using a plurality of types of correlation data, and that is particularly suited for grasping the position of a floor reaction force acting point related to a human being as a biped walking mobile body.
Moreover, it is another object of the present invention to provide a method of estimating a joint moment of a biped walking mobile body that makes it possible to grasp, in real time, the moment acting on a joint, such as a knee joint of a leg, by using the aforesaid estimated value of a floor reaction force acting point.